Gas analyzer and a method for operating the same

ABSTRACT

A gas analyzer having an analysis or sensor unit and having an electronic processing unit, and a method for operating such a gas analyzer. In order to achieve substantially improved safety both in handling corrosive and/or combustible and/or toxic gases in a not potentially explosive atmosphere (ex-free atmosphere), and in the operation of such an analyzer in an ex-atmosphere, the analysis or sensor unit as such is of non-explosive configuration and is arranged in a gas tight chamber around which a second chamber is arranged.

FIELD OF THE INVENTION

[0001] This invention relates to a gas analyzer having an analysis orsensor unit and having an electronic processing unit, and to a methodfor operating such a gas analyzer.

DESCRIPTION OF THE PRIOR ART

[0002] Many versions, and also many operating methods, are known for gasanalyzers having a sensing unit and an electronic processing unit. Inthis case, use is made of gas sensors which, depending on configuration,are sensitively set to one or other gases depending on which one isdesired for selective measurement. Electronic sensor systems, gelsensors, thermal conduction sensors and other similar sensors are knownfor this purpose. Solid electrolyte sensors are also known, inparticular for oxygen analysis.

[0003] Also known, however, over and above this are optical gas analysismethods in the case of which a cuvette flowed through by measuring gasis transradiated starting from a light source of specific radiationbands. Arranged on the side of the cuvette opposite the light source isa detector which picks up a measurement signal based on an optopneumaticeffect. The detector is sensitively set to the measuring gas componentto be measured, and measures the residual signal remaining in terms ofabsorption after passage through the cuvette. This is inverselyproportional to the partial pressure fraction of the measuring gascomponent in the measured gas sample. Because of this inverselyproportional relationship, so-called absorption spectroscopy is alsoinvolved here. Such methods are generally used as absorption photometerswith appropriate light sources

[0004] In the case of use in process measurement techniques, that is tosay in online measurement of industrial process cycles, for the mostpart gas samples are taken which are sent via the analyzer. Explosionprotection precautions are to be taken for the eventuality that thegases are toxic or combustible.

[0005] In chemical process engineering, however, it is frequentlynecessary to solve measurement tasks in which one or more gas componentsin corrosive and/or toxic and/or combustible gases are to be analyzed.As a rule, the extractive measurement techniques currently on offer havespecial properties in order to meet the requirements of measurementtechniques and safety. For this purpose, expensive use is made ofspecialists who are employed in potentially explosive atmospheres(ex-atmospheres) and also in corrosive and toxic gases together withhousing purging (pressurized enclosure) and a pressure tight enclosure,that are to be monitored. It frequently happens that some damage hasalready occurred before the service staff can intervene.

[0006] It is therefore the object of the invention to improve a gasanalyzer and a method for operating such in order substantially toimprove safety both in handling corrosive and/or combustible and/ortoxic gases in a not potentially explosive atmosphere (ex-freeatmosphere) and in the operation of such an analyzer in anex-atmosphere.

SUMMARY OF THE INVENTION

[0007] The solution according to the invention takes account in thiscase both for the gas analyzer and for the operating method both in thefirst case in which combustible gases are to be analysed in the ex-freeatmosphere, and of the second case, in which the combustible gas ispresent in an ex-atmosphere. In the second-named case, it is necessaryto add appropriate configurations, as described below.

[0008] Likewise to be distinguished are the gas analyzer groups alreadydescribed at the beginning in the prior art. These are, firstly, thegroup of optical gas analyzers and also others such as the group ofthermal conduction sensors and solid electrolyte or gel sensors.

[0009] The second-named case corresponds in essence to a gas analyzer inaccordance with Claim 1. The core of the invention there consists inthat in the case of the analysis of a toxic and/or corrosive and/orcombustible gas the analysis or sensor unit as such is of nonexplosive(for example intrinsically safe) configuration and is arranged in agastight chamber around which a second chamber is arranged. This case isthat of a gas analyzer with an integrated sensor unit and integratedprocessing unit.

[0010] However, these are arranged in a common housing in separate partsof the same. The sensor region arranged inside the housing iscorrespondingly provided with a non-combustible sensor which is arrangedin a first chamber, the second chamber then being arranged around thisfirst chamber and thus being placed between a first chamber, containingthe sensor, and the remaining space, in which the electronic system isarranged. This yields an appropriately ex-protected separation betweenthe sensor chamber and electronic system. If toxic or combustible orcorrosive gases are then fed to the sensor, they remain basically insidethe first chamber, which contains the sensor. For safety purposes, thesecond chamber, which is arranged around the first chamber, shields thelatter in turn.

[0011] It is provided in an appropriate refinement in the case of thisvariant apparatus that the second chamber is purged with an inert gas orwith air. If a leak were to occur in this case through the firstchamber, toxic or corrosive or combustible measuring gas would flow viathis leakage only into the second chamber, which is, in turn, purgedpermanently by an inert gas. The effect, in turn, is to dispose of theleakage gas into a closed purging gas system, the leakage gas therebybeing simultaneously substantially thinned by the purging. Consequently,in the way provided by the invention, not only is leakage counteracted,but leakage and/or the dangerous gas emerging because of the leakage canbe diluted until it is unobjectionable, and thereby be branded safe.

[0012] In a second independent device claim, the correspondinglyidentical methodology is applied to an analyzer which is based on anoptical detection method such as, for example, on absorption photometry.In this case, the element of corresponding consideration is the cuvette.The cuvette contains a measuring gas inlet and a measuring gas outlet.That is to say there is no gas contact with the detector as such, andthe cuvette remains a closed system. In order now to fulfil theex-protection preconditions in the way according to the invention, thesaid cuvette is surrounded either partially or completely by a secondspace.

[0013] A purging gas is fed inside this second space or the secondchamber, if the cuvette is defined as a first chamber, and appropriatelydischarged again. The purging gas used must fulfil two preconditions inthis case. Firstly, the purging gas must be inert or have at leastessentially such properties, and, secondly, it is not permitted toeffect any appreciable absorption of that radiation band which isdirected sensitively to the measuring gas. The general absorption whichoccurs through the plurality of the windows now occurring can be takeninto account by prior gauging or by calibration. Of course, it is alsopossible, going beyond this, also to take account of absorptive purginggas as well by appropriate calibration.

[0014] The same holds for the case of leakage and for the ex-protectionas such as did for the first-named embodiment. If a leakage occurs inthe critical region leading the toxic or corrosive or combustiblemeasuring gas, specifically in the cuvette, the leakage gas enters onlythe second space, which surrounds the measuring cuvette. Since thisspace or this chamber is, in addition, permanently purged by means ofpurging gas, as in the first example there is a steady thinning of thecritical gas. Likewise, the critical gas is led out of the system, andpossibly out of the ex-atmosphere.

[0015] As already mentioned, it holds for both variants that the secondchamber is purged with inert gas or with air.

[0016] Furthermore, according to the invention it is advantageouslyprovided both for the first and for the second variant that a pressurehigher by comparison with the first chamber is set in the secondchamber. This also produces a delimitation in terms of gas dynamics bycomparison with gas possibly escaping from the first chamber.

[0017] Furthermore, it is advantageously provided both for the first andfor the second variant that a flow sensor is used for monitoring thepurging gas. The purging gas flow can be monitored by means of thissensor and sensitive warning sensors which, as the case may be, areconnected downstream can detect critical gas compositions which can, inturn, have a regulating effect on the purging gas flow.

[0018] Both examples named so far relate essentially to the use of acombustible (possibly an explosive) gas in the ex-free atmosphere. Thatis to say, the ex-atmosphere exists only inside the analyzer, and iskept away from the electric systems with the aid of appropriatemeasures.

[0019] However, a second field of use is yielded by use in the so-calledex-atmosphere. In order to render such devices capable of this, as well,the devices as such are additionally protected overall in the outerregion by secondary ex-protective measures (for example pressurizingenclosure, pressuretight enclosure).

[0020] However, it is important to note in this case that the inventionis essentially directed firstly to the use of toxic or corrosive orcombustible gases, which are fed to the analyzer, initiallyindependently of whether the environment is in the potentially explosiveatmosphere or the not potentially explosive atmosphere. Thesecond-mentioned case concerns the handling of toxic or corrosive orcombustible gases inside the analyzer, in which case the latter is alsoarranged, in turn, in an ex-atmosphere.

[0021] With reference to a method for operating such a gas analyzer, itis provided according to the invention that in the case of analysis of atoxic or corrosive or combustible gas a space arranged around theanalysis or sensor unit is flowed around or through by a purging gas, anoverpressure being set in the purged space by comparison with theanalysis gas space. Consequently, for safety reasons, appropriatepressure gradients are set up which reliably prevent leakage gas fromescaping into the purging gas path and thus into the environment.

[0022] It is advantageously provided, furthermore, that purging isperformed via a regulator by virtue of the fact that fractions of toxicor corrosive or combustible gas components in the purging gas can bedetected by a sensor and, thereupon, the throughput of purging gas canbe increased under regulation.

[0023] It is advantageously provided, furthermore, that a change in thepurging gas flow or in the pressure is recorded in the test record forlater correction, if appropriate.

[0024] It is possible thereby to achieve an influence which is to becorrected accordingly, in particular in the case of optical gas analysismethods. It is possible to detect at least in which time phase themeasurement results are possibly unreliable.

[0025] In a further advantageous embodiment, it is specified that theentire system is caused to shut down in the event of the detection of anescaping gas.

[0026] In a last advantageous refinement, it is provided thatunderpressure purging can also be performed. That is to say, in thiscase the pressure of the purging gas in the second chamber is lower thanthe pressure in the first chamber, which leads the measuring gas. Thisresults at the same time in purging and, correspondingly, extraction.

DESCRIPTION OF THE DRAWING

[0027]FIG. 1 shows a design according to the invention with a cuvette.

[0028]FIG. 2 shows an embodiment according to the invention with asensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS(s)

[0029]FIG. 1 shows the use of the invention in terms of apparatus in thecase of absorption photometry, by way of example. In this case, thesystem purged by the measuring gas is the measuring cuvette 1 as such.The latter comprises a tubular element having a measuring gas input anda measuring gas output A. The entry window for the radiation from aradiation source 10 is in the region of the inlet E, and the outletwindow for the radiation passing the cuvette is in the region of themeasuring gas exit A, said radiation then being led to the detector 11.

[0030] Overall, the cuvette 1 is surrounded respectively by a secondchamber 2, 3, at least in the region of the window. Since otherwise thecuvette comprises a closed metallic tube, leakages can occur only at thebuilt-in windows. Consequently, a purging chamber can be provided onlyupstream of the entry window, and a purging chamber can be providedupstream of the exit window. In this case the two component chambers 2,3 are connected at the entry window and at the exit window to a gas linesuch that the two component chambers 2, 3 can be flowed through seriallyby the purging gas. However, for the purpose of enhanced protection ofthe system, the entire cuvette can also be provided on the outside witha closed second chamber to which purging gas is applied, or throughwhich purging gas is passed, as appropriate. In this case, a leakage inthe cuvette region leads only to the critical gas escaping into thepurging chamber.

[0031] A purging gas monitoring unit 5 having a sensor 6 and built intothe purging system monitors whether leakage gas occurs. If this happens,the purging or the purging throughput can be increased. This holds, inparticular, for the case of overpressure purging in which the pressurein the purging chamber region is higher than in the cuvette region.However, it is also possible to purge using underpressure, in which casethe purging gas pressure is lower than the gas pressure in the cuvette.In the second-named case, the detection of a leakage gas in the purgingsystem can lead to a further throughput, which can also lead to alowering or to a further lowering in the pressure in the purging system.

[0032]FIG. 2 shows a gas analyzer having a sensor unit and a processingunit in a housing 20. A non-explosive (for example intrinsically safe)sensor is arranged in a first sensor chamber 30 for the case in whichonly combustible gas is used. The toxic or corrosive or combustiblemeasuring gas is introduced into this sensor chamber 30 and extractedtherefrom. The sensor chamber 30 is surrounded in the way according tothe invention by a second chamber 40 which can optionally be purged.This second chamber 40 is a hermetic space between the sensor chamber 30and the housing 20 containing the electronic system. The escape ofcorrosive or toxic or combustible gas towards the analyzer is therebyprevented. The purging gas system operates in the same way as alreadymentioned in the above-named example.

[0033] For the purpose of using the two analyzers in accordance withFIG. 1 and FIG. 2 in a potentially explosive atmosphere, the system canbe further protected by secondary ex-protective measures (for examplepressurizing enclosure, pressuretight enclosure). It is possible overallto provide an emergency shutdown unit which, upon leakage of themeasuring gas, shuts down the entire system.

[0034] It is to be understood that the description of the preferredembodiment(s) is (are) intended to be only illustrative, rather thanexhaustive, of the present invention. Those of ordinary skill will beable to make certain additions, deletions, and/or modifications to theembodiment(s) of the disclosed subject matter without departing from thespirit of the invention or its scope, as defined by the appended claims.

What is claimed is:
 1. A gas analyzer for analyzing a toxic and/orcorrosive and/or combustible gas comprising: (a) a gas tight chamberaround which a second chamber is arranged; (b) an analysis or sensorunit of a non-explosive configuration arranged in said gas tightchamber; and (c) an electronic processing unit.
 2. A gas analyzer of thetype that uses the principle of optical gas analysis comprising: (a) anappropriate measuring cuvette flowed through by a measuring gas; saidcuvette having a window region and said cuvette surrounded either onlyin said window region or overall by a further chamber when gas analyzeris analyzing a toxic and/or corrosive and/or combustible gas; and (b) aprocessing unit.
 3. The gas analyzer of claim 1 wherein said secondchamber is purged with inert gas or air.
 4. The gas analyzer of claim 2wherein said surrounding further chamber is purged with inert gas orair.
 5. The gas analyzer of claim 1 wherein said second chamber has apressure higher or lower by comparison with said gas tight chamber. 6.The gas analyzer of claim 3 wherein said second chamber has a pressurehigher or lower by comparison with said gas tight chamber.
 7. The gasanalyzer of claim 2 wherein said surrounding further chamber has apressure higher or lower by comparison with said cuvette.
 8. The gasanalyzer of claim 4 wherein said surrounding further chamber has apressure higher or lower by comparison with said cuvette.
 9. A methodfor operating a gas analyzer having an analysis space comprising eitheran analysis or sensor unit or a measuring cuvette for analyzing a toxicand/or explosive gas comprising the step of: flowing around or through aspace arranged around said analysis or sensor unit or said measuringcuvette a purging gas to create a purged space having a pressuredeviating from said analysis space.
 10. The method of claim 9 furthercomprising the step of sealing said entire gas analyzer off from saidthe outside in a pressure tight fashion so that gas analyzer can be usedin an explosive environment.
 11. The method of claim 9 wherein said gasanalyzer has a measuring system and said purging gas is supplied from asystem said method further comprising the step of regulating saidpurging gas flow when leakage gas from said measuring system enters saidpurging gas system.
 12. The method of claim 10 wherein said gas analyzerhas a measuring system and said purging gas is supplied from a systemsaid method further comprising the step of regulating said purging gasflow when leakage gas from said measuring system enters said purging gassystem.
 13. The method of claim 9 further comprising the steps ofpicking up changes in said purging gas flow or the pressure of saidpurging gas and storing said changes in a test record in a fashioncorrelated with the measured date picked up at these instants.
 14. Themethod of claim 9 further comprising the step of shutting down as anemergency measure said purging gas flow in the event leakage gas isdetected in said purging gas system.